Asphalt is inexpensive, has a relatively high penetration value when applied to most porous surfaces, and is relatively weather-resistant and water-impermeable. As a result, asphalt has traditionally been used as a major component of protective coatings, films, and membranes. Water-based asphalt emulsions has been used for a wide array of products including waterproofing membranes, paving and roofing products, joint sealants, specialty paints, electrical laminates and hot melt adhesives. In addition, water-based asphalt emulsions have been used as diluents in the manufacture of low-grade rubber products, as diluents for the disposal of radioactive waste, for hot-dip coatings, and for water-retention barriers. For many of these applications, the water based asphalt emulsion is modified by inclusion of a hydrocarbon polymer such as natural rubber. The coating that results when such a modified product is applied to a substrate and allowed to dry has improved performance properties.
Asphalt emulsions, in their most basic form, are made by melting solid asphalt, typically at a temperature between 210-300° F., and then mixing the molten asphalt with water and a dispersant system. Such mixing, typically, is done in a colloid mill under high shear and high speed. If the emulsion is to be used as a waterproofing coating, hydrocarbon polymer emulsions/latexes such as natural rubber, styrene butadiene rubber (SBR), acrylic, etc., typically, are then added to these emulsions to give the properties that are desired. Since the resulting blend (asphalt emulsion plus hydrocarbon polymer emulsion/latex) typically requires an alkaline stabilizer such as ammonium hydroxide, the coating compositions are often neutral to alkaline in nature. Although, it is also possible to add the desired hydrocarbon polymer emulsion to the asphalt emulsion in situ, this is more difficult and rarely done.
Water-based asphalt emulsions, including those that comprise a hydrocarbon polymer emulsion or suspension such as a rubber latex, cure through moisture evaporation and subsequent coalescence of the dispersed particles. Even though these materials skin over in a relatively short period of time, the skin, generally, is not tough enough to withstand contact with water as in rainfall for exterior applications. Rain erodes the skin and washes out the uncured material underneath. Accordingly, application instructions for such materials generally suggest not applying the emulsion to a substrate if rain is a possibility within several hours of application. Moreover, the time required to cure through the entire coating composition may be unacceptably long or not occur at all. Such difficulties limit the thickness of the asphalt based coating compositions that can be applied to the underlying substrate. Because of the long drying time, the standard practice in the industry is to add a salt, such as calcium chloride during application to “break” the emulsions. The salt reacts with the ionic groups in the emulsion, causing the emulsion to destabilize and coagulate faster.
Non-water-based weather resistant coatings may also be prepared by combining polyurethane extenders and isocyanates to an asphalt material. However, the blend has to be heated, generally, from 80° C. to 120° C. Such methods are cumbersome and require special equipment on the job site.
Accordingly, it is desirable to have new systems and methods for preparing water based asphalt-containing coatings, films, and membranes Methods and systems that provide water-based asphalt coating compositions that dry more quickly, and thus achieve more rapid wash out resistance are desirable. Methods and systems that provide water-based asphalt-containing coating compositions with a relatively rapid cure through are also desirable. A rapid cure through of the coating compositions allows for reduced time on a job site, weight bearing loads sooner, pedestrian traffic sooner without detrimental effects to the physical integrity of the coating. In addition, a rapid cure through also enables a thicker layer of the coating composition to be applied as a single (i.e., in one step) as opposed to multiple layers to achieve the same thickness.